08.0195-1broch engels 2 kol.indd

Elevator planning for high-rise buildings
Elevator planning for high-rise buildings
High-rise buildings exist by the grace of elevators, and not
governor and safety brake in 1854, elevators suddenly
The feasibility of high-rise construction plans in the Netherlands
is most often restricted by soil conditions, investment risks
associated with such large-scale projects and reticence among
future tenants to commit to projects ahead of construction. In
the Netherlands, buildings taller than 150 m (490 ft) are purely
showcase projects. Project developers interested in a return on
their investment generally turn to other types of development.
became a safe and viable option for transporting people and
TALL, TALLER, TALLEST
vice versa. In a functional context, a tower’s elevator core is
the building’s main artery, and in a constructional context,
its spine. When Elijah Graves Otis invented the over speed
were no longer the limiting factor in the construction of highrise buildings. Since then, high-rise construction has spread
like wildfire across the globe. Principally in North America
but increasingly in Asia, the limits are being pushed ever
higher. The Taipei 101 measuring 509 m (1,670 ft) is currently
the world’s tallest finished building, but this year, the first
tower measuring over 800 m (2,625 ft) will be completed in
Dubai.
REGIONAL LIMITATIONS
Various issues determine the practical limitations for high-rise
construction around the world. These include:
• financial considerations (labour and ground costs)
• construction time
(phases, investment risk and permitted daily work hours)
• soil conditions (foundations)
• seismic/wind hazards
• accessibility/mobility at ground level
• regulations (construction, daylight access)
• energy consumption and efficiency
• prestige
There are several plans in the pipeline to top the current Dutch
high-rise record holder, the Montevideo residential tower block
in Rotterdam, that was built in 2005 and measures 152 m (499
ft). The Maastoren building is currently under construction in
Rotterdam that will measure 164 m (538 ft), and preliminary
plans have been discussed for the construction of a tower
block in Utrecht, called the Belle van Zuylen, that would measure
242 m (794 ft).
Elsewhere in Europe, restrictions are different, especially in
London, Frankfurt and Moscow where buildings are 50–100%
taller than those in the Netherlands. One Canada Square at
Canary Wharf in London measures 235 m (771 ft) and various
plans have been approved for the construction of tower blocks
measuring 250 to 300 m (820 to 985 ft) over the next ten years.
The tallest building in Frankfurt is the Commerzbank at 259 m
(850 ft), but the Millennium Tower that is still in its planning
phase will be 369 m (1,211 ft) tall. The tallest building in Europe
is in Moscow, the Triumph Palace measuring 264 m (866 ft).
Within the next two years, a further four buildings topping 300 m
(984 ft) will be completed including the 380 m (1,247 ft) tall
Mercury City Tower. The tallest European project currently under
construction is also in Moscow, the Russia Tower. This building
will be 612 m (2,008 ft) tall.
In North America and Australia, construction companies have
many years of experience building high-rises above the 250 m
(820 ft) mark. Since 9/11, the Sears Tower in Chicago is the
tallest skyscraper in North America measuring 442 m (1,450 ft).
The WTC in New York City used to measure 508 m (1,867 ft). In
New York City, the Empire State Building is now the tallest
skyscraper at 381 m (1,250 ft), but the Freedom Tower (currently
under construction on the site of the former WTC) will reclaim
the title for the continent’s tallest tower block at 541 m (1,775 ft).
Throughout New York, Chicago and Toronto, there are dozens
of buildings topping the 250 m (820 ft) mark.
In Australia, the maximum height for skyscrapers lies between
250 and 300 m (820 and 985 ft) with one solitary exception, the
Q1 residential tower block in Gold Coast City measuring 323 m
(1,060 ft).
Millenniumtower Rotterdam (132 m)
In recent years, Asia has taken a clear international lead in field
of high-rise construction. Eight of the ten world’s tallest buildings are currently situated in Southeast Asia. Predominantly in
Dubai and China, ultra-high-rise towers appear to be sprouting
out the ground like mushrooms. Buildings measuring between
300 and 400 m (985 and 1,312 ft) are the norm in certain areas of
Southeast Asia, and the world’s three largest finished buildings
can also be found there, the Taipei 101 at 509 m (1,667 ft) and
the Petronas Twin Towers in Kuala Lumpur at 492 m (1,614 ft).
There are currently an additional four towers of between 450 and
600 m (1,475 and 1,970 ft) under construction and another dozen
of between 500 and 600 m (1,640 and 1,970 ft) on the drawing
board.
Despite these valiant Southeast Asian efforts, the tallest building
in the world will soon be standing in the Middle East – the 818 m
(2,651 ft) tall Burj Dubai building currently under construction in
Dubai and due for completion in 2008. This frenzied hotbed of
high-rise construction will see an additional twenty tower blocks
measuring between 350 and 500 m (1,150 and 1,640 ft) before
2010. However, Kuwait and Dubai are pushing the envelope even
further with proposals for 1000 to 1200 m (3280 to 3940 ft)
high…
ELEVATOR PLANNING
Building access plays a crucial role in the development and
feasibility of high-rise construction plans. Internal transportation
systems function as the building’s main artery, determining the
functionality and quality of life within the tower block, yet they
also result in a considerable loss of rentable floor space on each
level. Moreover, the elevator core is often the building’s support
structure, especially in narrower constructions. For this reason,
it is very important that a traffic flow specialist be involved in the
initial orientation phases of a high-rise construction project, as
well as the developer, architect and structural engineer. Specifications for internal transportation must be drawn up whereby
routing and usage remain logical, while occupying as little space
as possible. Above all, the capacity required for stairs, elevators
and shafts need to be determined.
CAPACITY AND WAITING TIME ANALYSIS
When designing an elevator system for either low-rise or highrise buildings, the same initial estimates can theoretically be
applied to its usage and function as for any other project. The
building’s function (office space, residential, hotel or a combination of these), the probable population and peak demand (either
the up-peak, down-peak or lunch-peak) form the determining
factors. The following parameters need to be determined in
Traffic Flow Intensity Parameters
Function
Population
Occupancy
Office Space
1 x workplace per 18-25 m² (190 270 sq ft) GFA, or 60-85% enter in the morning up-peak
1 x workplace per 10-15 m² (110 160 sq ft) NFA
Hotel
1.2-1.5 persons per room
90% room occupancy
Residential
Based on the Dutch NEN 5080
(comparable with CIBSE), dependent on the
number of rooms per apartment:
40-60% leave in the morning down-peak
1.25 persons in a 1 or 2-room apt.
2.00 persons in a 3-room apt.
2.75 persons in a 4-room apt.
3.50 persons in a 5 or more-room apt.
Educational
1 x person per 4-7 m² (45-75 sq ft) NFA
45-75% arrive during the first or second
lesson period
Table 1: Indication of population, occupancy and peak demand for various building functions (Europe).
Skyline Chicago
Peak Demand
The up-peak is generally always
indicative (12.5-18% per five
minutes), unless the restaurant is
not located on the ground floor.
The morning down-peak is
determinant. Descending and
ascending breakfast traffic plus
downwards checkout traffic,
together 14-18% per five minutes.
The down-peak is indicative
(3-6% per five minutes).
The up-peak and/or the peak
during lesson changeovers are
indicative (15-25% per five
minutes).
Taipei 101 Elevator Technology
The tallest building in the world is currently the Taipei 101 measuring
509 m (1,670 ft). This office block houses fifty elevators of which
thirty-four are double-deckers and two are the fastest elevators in the
world. Total investment in elevator technology for this building totalled
approximately US$85 million.
The tower has two shuttle elevators for public access to the
observation deck on the 89th floor. These elevators have been
officially recognized by the Guinness Book of Records as the fastest
elevators in the world. With full loads, the ascent speed reaches
a maximum of 16.8 m/s (55 ft/sec) or nearly 60 km/h (37 mph).
Descent speeds measure 10.0 m/s (33 ft/sec) or 37 km/h (23 mph). In
comparison, the fastest elevators in the Netherlands travel at 6.0 m/s
(19.5 ft/sec). These are located in the Delftse Poort (Rotterdam), the
Rembrandttoren (Amsterdam), the Hoftoren (The Hague) and the WTC
(Amsterdam).
Elevator cars in these shuttles are fitted out as airtight pressure cabins
and equipped with pressure regulation systems similar to those used
in aircraft. This allows for a gradual change in pressure over the
elevator’s height to alleviate the pain that can be caused to passengers’
ears. Pressurization on descent is also the reason why the elevators
descend more slowly than they ascend. (Pressurization is more painful
for the ears than the depressurization that occurs on ascent). Elevator
cars are fitted with upper and lower capsule-shaped spoilers to provide
aerodynamic streamlining. These ensure that the air stream flows
smoothly around the moving elevator car saving energy and reducing
interior shaft airflow-induced noise levels.
Vibration within the car has virtually been eliminated by implementing
a tri-axial, active-control roller guidance system for suspending cars
in their tracks. Active mass damping has also been fitted to each
elevator to minimize lateral movement. Car movement experienced as
two elevators pass one another in opposite directions at full speed has
virtually been eliminated. Thanks to these measures, comfort levels
can only be described as phenomenal, certainly given their exceptional
speeds. The safety braking system, that operates in the event that the
car exceeds nominal speeds by more than 10% for whatever reason
(e.g. a broken cable or driveshaft, or traction failure), is fitted with
brake pads made of a silicon nitrite ceramic compound that brings the
car to a standstill swiftly and safely.
The office block (floors 9 through 84) is accessed as though it were
made up of three individual building segments each of 112 m (367 ft)
stacked one on top of the other. Transportation to and from the sky
lobbies on the 35th and 59th floors is provided by ten high-speed,
double-deck elevators (weighing 4,080 kg (8,995 lb) and holding up
to twenty-seven passengers per car) that shuttle their passengers
non-stop to their transfer levels. Each of the three sub-segments is
fitted with its own local double-deck elevator system (weighing 2,700
kg (5,952 lb) and holding up to eighteen passengers per car) of which
four are low-rise and four are high-rise systems. The use of doubledeck elevators doubles the transportation capacity per shaft, especially
to and from the sky lobbies. These double-deck elevator cars also
incorporate a technological innovation. The two cars are suspended
independently of one another in a frame to allow for inter-dependent
movement, which compensates for local floor height differences.
In addition to the public shuttle elevators to the observation deck on the 89th floor and the doubledeck elevators to the sky lobbies, the Taipei 101 also houses four exclusive passenger elevators to the
sky restaurant and executive club, four general-purpose goods and fire fighting elevators, six car park
elevators, eleven passenger elevators at the base for commercial purposes and fifty escalators.
sequence for the anticipated traffic flow,
given the building’s envisaged function:
• population (number of employees and/
or residents)
• occupancy (presence/
simultaneousness)
• peak demand (indicative traffic flow
peak)
where, required capacity = population x
occupancy x peak demand (expressed as
a % of the occupancy per 5 minutes)
Table 1 shows guidelines for population,
occupancy and peak demand values for
various building functions. These are
based on European conditions, however
regional differences can be significant.
It is essential that a project-specific
estimate be made of these parameters
based on the project’s individual characteristics, conditions and ambitions.
The building should be examined to
establish the following criteria, which
should then be incorporated correctly into
traffic flow models:
• height of the building and its individual
storeys
• distribution of the population throughout the building
• main entrance level(s) (points of entry
and exit)
• distribution of population over elevator
groups (if the same destination can be
reached using more than one group)
• stair usage
This allows the building’s anticipated
traffic flow to be established and a
corresponding elevator configuration to
be specified. Initially, an estimate of the
elevator group requirements is made on
the basis of past experience. This
estimate should take the following into
consideration:
Primary Considerations:
• number of elevators per group
• nominal elevator load capacity (based
on car floor area)
• realistic car occupancy
• nominal elevator speed
Secondary Considerations:
• elevator acceleration
• door times (opening and closing, door
type, dimensions, et cetera)
• entry and exit times (dependent on type
of user, free passageway and car
occupancy)
SPECIFICATIONS FOR ADEQUATE
TRAFFIC FLOW MANAGEMENT
The following issues should be taken into consideration in order
to determine whether adequate traffic flow management exists in
high-rise buildings:
• Primary Considerations: Peak demand capacity must be
sufficient, i.e. the elevator configuration should provide
sufficient transportation capacity to deal with the demand.
• Secondary Considerations: Waiting times should remain
acceptable even in peak periods (not only on main levels, but
throughout the building)
• Tertiary Considerations: Elevator speeds must be high enough
to reach the destination within an acceptable time (specifically
on direct journeys without stops)
• Supplementary Considerations:
− Robustness (failure): In the event of elevator malfunction
and/or maintenance, or use of an elevator for goods or
moving home/office, the remaining transportation capacity
should remain sufficient to deal with continued demand.
− Robustness (deviations from norm): If transportation
capacity is rated to saturation tolerance thresholds, then
any deviations or incorrect estimates concerning traffic flow
can lead to greatly increased waiting times and even
capacity shortages.
− Durability (design): Elevator configurations should be
designed to deal with any future traffic flow changes that
might reasonably be anticipated. If calculations show low
occupancy and low peak demand, then the number of
elevators can be reduced, but this may result in the building
being unsuitable for rental to future tenants with a different
profile (i.e. higher occupancy, e.g. a call centre with high
peak demands at fixed times). This entails that a certain
degree of over-capacity should be incorporated into the
design.
− Requirements, or necessity, to include separate goods
elevators and/or fire fighting elevators in towers, and
consideration as to whether these may be integrated into
passenger elevator group(s).
The considerations listed above can – within reason – be
subjected to considerable influence. A common mistake is often
made when confronted with unfavourable outcomes, i.e. traffic
flow/elevator capacity mismatches. Instead of adjusting the
basic elevator concept, the basic assumptions, which cannot
be influenced, are tweaked to force a match, e.g. entry and exit
times, car occupancy, stair usage, etc. Sometimes, even
population, occupancy and peak demand figures are retroactively adjusted down to force a match with the elevator system
design’s maximum attainable capacity (both financial and
spatial). This is in fundamental denial of original basic principles
whereby reality is adjusted to match the design. A more correct
and realistic approach to this conundrum is to adjust the
building’s properties – height, occupancy per storey, reduced
number of main stops, separate car park elevators, escalators,
restaurant location, etc. – or to adjust the elevator system’s
primary parameters – number of elevators, load capacity,
nominal speed, et cetera.
Acceptable Performance
The ultimate assessment criterion for acceptable traffic flow
management always remains the waiting time and/or the
destination time. There are no hard and fast standards for
acceptable waiting times, only experiential data. Guidelines for
acceptable waiting and destination times should be determined
on a project-by-project basis taking into account the building’s
Elevator simulation example.
function, its ambitions and the available budget. Table 2 offers
an illustration of various experiential data concerning waiting
times for various building functions and ambitions.
Peak Waiting Time
Function
Office Space
Hotel
Residential
Healthcare
Excellent
≤ 25 sec
≤ 20 sec
≤ 35 sec
≤ 30 sec
Good
≤ 30 sec
≤ 25 sec
≤ 40 sec
≤ 40 sec
Moderate
≤ 35 sec
≤ 30 sec
≤ 45 sec
≤ 50 sec
Table 2: An indication of acceptable waiting times for various building functions.
An indication of nominal travel times (travel height / nominal
speed) acceptable for an office block is somewhere between 25
and 30 seconds, and for housing, between 30 and 40 seconds.
The nominal travel time can be viewed as a near constant value
that should be used to determine the nominal elevator speed.
CALCULATION VERSUS SIMULATION
Whereas round-trip time calculations suffice for simple low to
medium-rise office buildings, simulations are an absolute
requirement for high-rise traffic flow analysis.
Traditional round-trip calculations examine the theoretical
total cycle time for a single elevator during up-peak demand.
Estimates are made using statistical probabilities as to how
many stops are made on the ascent and descent for a complete
round trip, where the elevator is assumed to have a full passenger load at the main entrance level. By evaluating the sum of
time lost for each individual component of the cycle (ascent,
descent, exiting, entering, acceleration, deceleration), a total
round-trip time (RTT) can be calculated. The theoretical roundtrip time can be defined as the time elapsed between two
successive arrivals of the same elevator at the main entrance
level. By dividing the RTT by the number of elevators in a group,
the interval (INT) can be derived and is defined as the time
elapsed between two successive arrivals of any elevator at the
main entrance level. The INT is generally used as a measure of
an elevator group’s performance. In general, this should be less
than 30 seconds.
Through dividing the realistic elevator car occupancy at departure
from the main entrance level by the interval time, an indication of
the elevator group’s transportation capacity can be calculated.
Although the round-trip time provides an accurate estimate for
Residential towers Hong Kong
traffic flow or storey is simulated by a random generator that
inputs a realistic and reliable flow to the virtual elevator system.
However complex or non-compliant the individual flows may be
(inter-floor traffic flows, bi-directional traffic patterns, simultaneous goods flows, et cetera), they can all be modelled for any
given elevator system. The virtual elevator system deals with the
input requests as if it were a real system, and waiting times and
destination times are recorded. Results are stored in a database,
which can be queried to draw conclusions about average and
maximum passenger waiting and destination times during peak
demand. Results for various traffic flow management scenarios
for multiple elevator configurations can then be evaluated and
compared to one another. By applying an iterative process,
elevator configurations can be fine-tuned to arrive at the optimal
solution for any given building. Using elevator simulations, it
becomes evident that the interval is no longer the key performance indicator, but that waiting and destination times are now
the determining factors.
elevator groups in many instances, this approach may only be
applied under the following conditions:
• An RTT calculation can only be used for simple up-peak
demand. It cannot therefore be applied to residential tower
blocks (morning down-peak demand), hotels (morning bidirectional peak demand) and office blocks at lunch times
(bi directional peak demand).
• An RTT calculation can only be used where there is one main
entrance level, which excludes buildings with a subterranean
car park, with a restaurant on a level other than the main
entrance level, or with other main interchange levels.
• An RTT calculation can only be used where there is no
disruptive inter-floor traffic flow during the determining uppeak demand.
• An RTT calculation can only be used where all elevators in a
group are identical.
An additional problem is that the ultimate RTT analysis criterion,
the interval, is often an unreliable indicator for the actual waiting
time. This is certainly the case when transportation capacity is
inadequate; intervals can remain acceptable whereas waiting
times increase drastically. Additionally, the use of the interval as
an elevator group performance indicator is fundamentally flawed
for elevator groups with destination control (see inset). Where
destination control has been implemented, passengers sometimes have to wait for elevators travelling to other destination
zones to pass, before their designated elevator arrives. By
definition, this invalidates the already dubious relationship
between interval and waiting time for destination control entirely.
The abovementioned limitations – plus the fact that high-rise and
stacked construction is becoming ever more popular – means
that elevator planning is increasingly performed by means of
simulation. Traffic flows, the building and elevator groups are
modelled within one integrated simulation environment. Each
In short, elevator planning in high-rise buildings is an iterative
and time-intensive process. It is crucial that the main features
of the elevator core configuration be set in stone as early as
possible in the design process. A thorough understanding of
elevator technology, control systems and simulation methods
are essential for estimating the required elevator configuration
capacity for high-rise buildings. It is only possible to derive a
balanced and reliable analysis of a building’s transportation
requirements with a good intuitive estimate of the usage and
the peaks in demand for the building’s envisaged functionality,
and the relative effects of the various parameters used in the
simulation method (sensitivity analysis). Correct assessment
of the effect of human behaviour as well as user experience,
access systems and access control also play an important role
in this whole process.
CHALLENGES INHERENT IN DESIGNING HIGHRISE ELEVATOR
SYSTEMS
The differences between capacity studies for low-rise and highrise construction are immense, in terms of both the depth of
analysis and the effort required. These differences can be
attributed to the following four points, in addition to the various
analysis methods mentioned above (see “Calculation versus
Simulation”):
• A wider variety of elevator configurations is possible for
high-rise construction than low-rise
A central elevator group is generally adequate for low-rise and
medium-rise buildings up to 70 m (230 ft) tall. There is,
however, a whole host of options available for managing
access within high-rise buildings depending on their height.
The essence lies in the benefits that can be gained by splitting
a building into elevator system zones, e.g. a two-zone layout
(low-rise/high-rise) or three-zone layout (low-rise/medium-rise/
high-rise). In buildings taller than about 200 m (650 ft), serious
consideration is given to a physical segregation of elevator
systems into multiple stacked towers. Lower tower zones are
served by elevators from the main entrance level and upper
zones are accessed by elevators boarded at sky lobbies
(transfer levels) reached by shuttle elevators. Passengers then
have to transfer to local elevators at these sky lobbies. The
higher the tower, the more elevator system segments are
incorporated (see Taipei 101 inset). If one of these options is
chosen, then fine-tuning is needed to determine the correct
positioning of the transfer levels, and the elevator loads and
speeds required. (see Specific Highrise Challenges inset for
further details)
SPECIFIC HIGHRISE CHALLENGES
Optimising traffic performance in high-rise:
Traffic handling is more efficient when the number of
destinations per elevator is reduced. This minimizes the
number of stops, the travelling distance and thus the time
required for the (empty) return ride. There are 3 basic
methods for reducing the number of destinations:
Method 1:
High-rise buildings (>150-200 m high)
are split up in separate stacked towers
(zones) to minimize continuous shafts
over the tower’s total height. To reach
the skylobby of the higher zone(s)
shuttle elevators are required.
Method 2:
Elevators in
local tower
zones are split
up in groups,
serving local
low-rise and
high-rise
floors. Low-rise and high-rise elevators in the same zone
serve the same home floor (ground floor or skylobby). For
methods 1 and 2, part of the optimization lies in finding the
optimal skylobby level and the optimal separation level
between low-rise and high-rise groups, to minimize the total
number of shafts.
This is an iterative process.
Method 3:
Destination control reduces the
number of destinations per car and
thus the number of stops per cycle.
This decreases the average travel
height and the cycle time. When
elevators
are
equipped with destination control,
this can even reduce the number
of elevators per group.
The real challenge lies in stacking
uniform cores from different zones
on top of each other by integrating
elevator pits and machine rooms in technical layers. This
results in consistent core lay-outs over the height, which is
advantageous for the
construction and minimizes
suboptimal office space
(pantries et cetera) in
redundant core areas.
Additional optimizing
possibilities are using
double deck elevators and
TWIN elevators. These can
further increase the traffic
capacity per shaft, usually
resulting in less shafts.
• Minor considerations can suddenly become far more
influential – striking the balance
The individual effects of each traffic flow parameter on
transportation capacity are many times greater for high-rise
construction than for low-rise. Marginal differences when finetuning parameters such as peak demand, population, door
times, entry and exit times, et cetera can all influence traffic
flow management to a high degree. The balance between
demand and handling is so sensitive that even the slightest
deviation can result in the need to change the entire elevator
system concept. Traffic flow management is nowhere near as
complex for low-rise construction as it is for high-rise.
• Tight margins – right the first time!
Designs for high-rise construction projects have to be right the
first time. There are never, or hardly ever, opportunities to
make subsequent changes. Retroactive changes to the basic
assumptions are near impossible without the design having to
be recalculated. The available design margins often have to be
made known in the preliminary design phase, if high-rise
construction plans are to become viable. This often conflicts
with the flexibility required in subsequent phases. The
freedom to make programmed or architectural changes are
minimal. If changes are made nonetheless, then the elevator
design and/or concept must be amended quickly.
• Various control systems available
A simple hall call collecting elevator control system is adequate for most low-rise buildings, but destination control
should be considered for high-rise buildings (see inset). The
quality and artificial intelligence level of the group control
system is then of critical importance, whereas these have far
less influence in low-rise buildings. Traffic flow pattern
recognition, adaptation of traffic flow management in response to these patterns and self-learning play an important role in
the selection of a suitable control system. The Twin Lift
concept (see inset) is also a consideration worth taking into
account.
TECHNOLOGY AND COMFORT
High-Speed Elevator Technology
Although there are no major differences with regard to suspension and guidance systems between high-rise and low-rise
elevator systems, there are other aspects to be considered that
complicate matters, such as system technology and passenger
comfort levels. Control system artificial intelligence levels, safety
requirements, load-bearing component ratings and subsequent
pricing increase almost exponentially in proportion to the height
of the building. The same applies to cable weight and energy
consumption.
High-speed elevators in high-rise buildings pose a serious
challenge with respect to the reciprocating air displacement in
elevator shafts. Air resistance results in not only higher energy
consumption levels, but the air being displaced past the car also
generates whining and whistling noises inside the car. To prevent
this, cars in high-rise buildings have to have aerodynamically
designed exteriors resembling a drop-like shape with spoilers to
channel air past the elevator. To prevent hammering sounds
caused by the passage of the elevator past the landing doors,
shafts have to be fully cladded between levels to create an even,
flush surface. Cars also needs to be soundproofed to reduce
noise emission levels within the car. Noise transmission through
car ventilation systems also needs to be minimized.
An additional problem associated with high-speed elevators is
the plunger effect caused by the car’s movement inside the
shaft. In high-rise buildings, it is essential that displaced air can
be interchanged between elevator shafts. A preferred option is
to suspend all elevators in one open shaft; however, this reduces
the structural load-bearing capacity of the elevator core. The
entire shaft then has to be fitted out to the same system
integrity, fire resistance and high-pressure ventilation levels
for all elevators. In practice, shaft partitioning walls are often
perforated, or interconnecting openings (bypasses) are incorporated at the top (headroom) and base (pit) of adjacent shafts to
allow the interchange of displaced air columns.
A robust car guidance system with meticulously aligned tracks
are essential for reducing vibrations to an acceptable comfort
level. Tracks must be rated for heavy-duty usage, guidance
surfaces and welds have to be totally flush, and mounting points
have to be positioned to within microns, as every irregularity in
the guidance system causes an unpleasant and uncomfortable
transverse vibration within the car at high speeds. High-quality
roller guidance systems are also required. To complicate matters
still further, the elevator guidance system must be able to
withstand the effects of the building settling and the response of
the building’s structure to thermal and climatic changes.
The pressure difference between the base and the top of a
building’s elevator shaft also plays an important role in elevator
design. To prevent the shaft acting like a chimney, and air
causing a whistling noise when passing door seals, elevator
shaft doors have to be made airtight, e.g. by implementing
interlocking labyrinth seals. At main entrance levels, direct
passage to the outside air should be eliminated by incorporating
Conventional versus Destination Control
Conventional elevator controls allow users to indicate their chosen direction
of travel by means of up and down buttons. Cars are typically filled in the
same order that user requests are received. The control system gathers
all requests for each travel direction, but does not know in advance which
destinations will be selected by users once inside the car. Chances are high
that there will be a large number of destinations entered for each round trip,
as well as a high probability that several elevators will simultaneously serve
the same range of destinations.
Destination control eliminates this problem because final destinations are
already selected by users when calling the elevator. This allows the control
system to cluster destinations for each car using dynamic zoning, thus
significantly reducing the travel time and the number of stops. Moreover,
not every elevator has to travel all the way to the top of the building on each
round trip. When calling an elevator, passengers are notified as to which
elevator will be transporting them. Destination control is optimized on the
basis of destination time (waiting time + travel time) and not on waiting time.
The total passenger destination time is reduced although the waiting time
often increases with respect to that for conventional control systems.
Destination control is ideal for situations in:
•
•
•
•
•
high-rise buildings where large dynamic zones can be defined
large elevator groups where multiple dynamic zones can be defined
buildings with high peak demand
buildings with marginal disruptive between-floor traffic flows
buildings with a fixed population that will become familiar with such
systems
Advantages of destination control include the following:
• passengers make fewer stops en route and arrive at their destinations
very quickly
double airlocks, et cetera. Elevator machine rooms should also
be made as airtight as possible, and despite the use of mechanical ventilation, no vents should open directly to the outside air.
Ride Comfort
Elevator comfort is principally determined by interior noise levels
and transverse car vibration. Cars should be designed to
suppress interior noise levels to less than 48–52 dB(A) for
superior ride comfort, as for low-speed elevators. Noise levels
above 60 dB(A) are generally acknowledged to be inadequate. In
contrast to low-rise buildings, high-rise buildings require
additional measures to reduce noise levels (see “High-Speed
Elevator Technology”).
Transverse car vibration also needs to be minimized to ensure
acceptable comfort levels. This imposes high demands on
suspension, track and roller guidance systems. At high speeds
greater than 3.0 m/s (10 ft/sec), additional technological and
alignment measures are vital to ensuring acceptable comfort
levels, in contrast to low-speed systems less than 2.5 m/s (8 ft/
sec), where little if any attention needs to be paid to such
matters.
To achieve improved comfort levels in high-speed elevator
systems, additional requirements are also imposed on axial
acceleration/deceleration (for smooth pick-up and braking) and
axial jerk (acceleration/deceleration build-up).
Pressurization and depressurization of the elevator car should
• car occupancy is lower and therefore more comfortable for passengers
• capacity is sufficient even during peak demand (14¬–18% of the population
per five minutes). Destination control can be used as a capacity booster
where additional capacity is achieved using existing elevator systems
• in some cases, destination control saves the need for an additional elevator
and elevator shaft
• given that passengers are assigned to an elevator, they can stand at the
correct location in the lobby allowing more flexibility in the layout of the
elevator core
• a reduced number of stops means that an increase in the elevator speed has
an even greater effect on dealing with traffic flows
Disadvantages of destination control include the following:
• waiting times are generally longer than for conventional control, even when
traffic flows are low (see graph)
• elevator users have to accept that sometimes, several elevators will come
and go before their assigned elevator arrives
• each user has to enter their destination, even for groups
• misuse and accidental usage (ghost passengers and missing passengers)
are seriously detrimental to traffic flow handling capacity
• not yet viable for public buildings, as the general public is still insufficiently
familiar with such systems
also be minimized. At descent speeds above 8–10 m/s (26–33 ft/
sec), car pressurization can be painful to passengers’ ears. The
absolute pressurization from start to end and the period over
which the pressurization persists both play a role. At extremely
high speeds, such as the Taipei 101 elevators that travel at 17 m/
s (56 ft/sec), elevator cars have to be fitted with fully pressurized
cabins similar to aircraft specifications. Although depressurization on ascent is generally experienced as being less painful
than pressurization on descent, this should also be regulated as
far as possible.
A lot of research is currently being conducted into the possibilities for and hazards associated with evacuation by elevators.
Even in the Netherlands, elevator evacuation is back on the
agenda since the publication of the SBR’s practical guidelines,
Brandveiligheid in hoge gebouwen [Fire Safety in High-rise
Buildings]. This topic will be receiving a lot of attention under the
auspices of the National High-rise Covenant currently being
drafted in collaboration with NEN.
A final consideration relating to journey comfort involves car
occupancy. This is not an issue specific to high-rise elevator
systems, but – according to European rule of thumb – should be
limited to a maximum of 70% of the theoretical load limit (based
on an average weight of 75 kg (165 lb) per person).
Elevator Evacuation
Everyone has always been taught not to use elevators in the
event of a fire or other emergency. In ultra-high-rise buildings
taller than 300 m (980 ft), full evacuation using the stairwells is
however a utopian dream. To evacuate an entire tower measuring 400 m (1,310 ft) would take one to three hours.
For this reason, two trends have become increasingly evident in
recent years, predominantly in Asia and Australia – evacuation
by zone and evacuation by elevators. Evacuation by zone
involves a phased evacuation whereby only the zone affected by
the emergency is evacuated, not the entire building. Each zone
has a designated evacuation level to which people can escape
by stair until the danger has passed. These evacuation levels
can maintain systems integrity for up to one hour and allow
escape flows to switch escape stairwells. The Taipei 101 has an
evacuation zone at the base of every eight-storey segment.
The second trend, evacuation by elevator, no longer reserves the
use of elevators for fire fighters and emergency personnel;
certain (or all) elevators are specifically designated for evacuation purposes. It is implicitly understood that such elevators are
subject to a host of additional safety requirements covering
systems integrity, fire resistance, control and monitoring. To
handle transportation under panic conditions, it must be
possible for elevators in emergency mode to operate according
to a different set of overload controls, door closing characteristics and load-non-stop conditions. It remains to be seen whether
it is feasible and/or sensible to increase descent speeds and
acceleration rates in such situations. In conclusion, it must also
be possible – using sophisticated building management
communication systems – to alter evacuation procedures on a
real-time basis, depending on the type and location of the
emergency, such that options for alternative evacuation routes
are made available (zoned, complete, bottom-up or top-down).
Checks would then be required to verify whether exiting at main
levels is a safe, viable option, or whether an alternative escape
route is required (consistent with the European NEN-EN 81-73).
Shafts should also be pressurised to remain smoke-free. It is
vital that this air is channelled from safe zones, i.e. guaranteed
smoke-free. Future options might include dynamic ventilation
systems that automatically search for areas from which safe,
smoke-free air can be channelled.
Twin Lifts
The ThyssenKrupp Twin Lift concept has been available for the past few
years and involves the operation of two separate elevator cars within one
shaft. The elevators use the same tracks and elevator shaft access points,
but have separate cars, drives, suspension and control systems. Triple-layer
mechanical end electronic safety systems ensure that the two cars remain
out of each other’s way. The upper car generally serves destinations in the
top half of the building and the lower car the bottom half – with destination
control. The lower car can only let on passengers at the main entrance level
once the upper car has departed, and is required to wait below the main
entrance level whenever the upper car needs to return to that level.
Depending on traffic flows, the twin lift concept provides an additional
capacity of approximately 30–40% per elevator shaft. This means that for
larger elevator groups fewer shafts are required.
Twin lifts are ideal for situations in:
• high-rise buildings with high peak demand
• buildings with large elevator groups
• buildings with a lot of between-floor traffic flows
Twin lifts can only be implemented under the following conditions:
• destination control is in use to dynamically keep cars out of each other’s
zones
• at least one conventional elevator must be included in the elevator group
for transportation from the lowest to the highest stop. This must also be
designated as the fire fighting elevator.
• a holding pit of at least 8–10 m (26–33 ft) deep must be available in
which the lower car can wait until the upper car has departed, before it
can let on passengers at the main entrance level. This could be a car park
or basement level, or the main boarding level could alternatively be moved
to the 2nd or 3rd floor, accessible by escalator.
‘Strijkijzer’ The Hague (132 m)
CONCLUSION
High-rise elevator systems demand meticulous and impartial
capacity analysis and detailed simulation. Not only should the
building, its population and peak demands be correctly modelled, but elevator configuration and physical and/or dynamic
zoning should also be determined. The correct choice of group
control system plays a vital role, as does the correct choice of
group sizing, elevator capacity and nominal speed. Given that
the elevator core forms the building’s load-bearing structure and
such factors are determined early in the design process, the
right choices have to be made first time round. There are few if
any opportunities to correct mistakes later. This demands
logistical and elevator planning insight, extensive expertise and
experience, and the application of correct safety margins. Using
simulations, safeguards must be in place to ensure that invalid
adjustments are not made to parameters when specifying traffic
flows.
A variety of additional technical measures is required to ensure
safety and comfort within the car at high speeds. Extremely high
demands are placed on the suspension, track and guidance
systems, and transmission and control systems must also be
heavy-duty, reliable and accurate. The group control system’s
quality and artificial intelligence levels ultimately determine
transportation efficiency. These issues cause high-rise elevator
system costs to increase proportionally by more than the square
of the building’s height. Even though Dutch high-rise buildings
may not even be considered high-rise from a global perspective,
high-rise elevator system logistics and technology should not be
underestimated. These issues require serious attention for
continued development of high-rise buildings in the Netherlands
given that increasingly taller buildings are being constructed and
evacuation by elevators is becoming inevitable.
Shuttle elevator Atomium Brussels
Author: Jochem Wit Msc.
Jochem Wit (1971) graduated from the Technical University (TU) in
Delft in 1995 with a degree in Mechanical Engineering, specializing in
Transportation Technology and Logistics.
After graduation, he went to work at Deerns Consulting Engineers BV
where he is team leader of the Transportation & Logistics expertise group,
a department specializing in elevators, escalators, moving walkways
(travelators), façade maintenance systems, baggage handling systems,
pneumatic dispatch systems, passenger boarding bridges et cetera.
Wit also heads up complex projects in the field of new transportation system
construction and renovation for the non/residential, healthcare and aviation
sectors. He specializes in performing capacity planning studies to determine
optimum elevator system configurations for buildings and specifically, traffic
flow studies for high-rise buildings and hospitals.
Wit is also a member of the Technical Workgroup for the National Highrise Covenant and chairs the Transportation System sub-workgroup. The
National High-rise Covenant being drafted in collaboration with NEN aims
to arrive at sector-specific agreements (so-called NTAs [Dutch Technical
Agreements]) relevant to high-rise construction projects in the Netherlands.
Several Deerns High-Rise Projects
Our complete high-rise project portfolio is available on request.
New Orleans & Havana, Rotterdam
Height:
Function:
154.7 m (508 ft)
residential, medical centre, office space,
museum and cinema
Floor Space: approx. 210,000 m2 (2,260,420 sq ft) GFA
Customer: Vesteda/TRS Ontwikkelingsgroep
Architect:
Cruz y Ortiz (Spain), Alvaro Siza (Portugal)
Status:
under development (2009)
Deerns:
concept and preliminary design
Ministries of Internal Affairs and Justice, The Hague
Height:
Function:
Floor Space:
Customer:
Architect:
Status:
Deerns:
Height:
109 m (358 ft) including antenna 128m
(420 ft)
Function:
office space
Floor Space: approx. 32,700 m2 (351,980 sq ft) GFA
Customer: BPF Bouwinvest
Architect:
Kraaijvanger Urbis (R. Ligtvoet)
Status:
completed in 2004
Deerns:
complete design
Mahler4, Amsterdam
146.5 m (481 ft) (x 2)
office space
105,000 m2 (1,130,210 sq ft) GFA
Rijksgebouwendienst
Kollhoff (Germany)
under construction (2011)
complete design
Millennium Tower, Rotterdam
Height:
132 m (433 ft) including antenna 149 m
(489 ft)
Function:
hotel and office space
Floor Space: approx. 39,000 m2 (419,790 sq ft) GFA
Customer: Kintel Rotterdam BV
Architect:
Webb Zerafa Menkès Housden (Canada)
Status:
completed in 2000
Deerns:
schedule of requirements and design
supervision
Woontoren Strijkijzer, The Hague
Height:
Function:
Floor Space:
Customer:
Architect:
Status:
Deerns:
Prinsenhof Tower E, The Hague
132 m (433 ft)
residential
approx. 30,000 m2 (322,920 sq ft) GFA
Vestia/Ceres Projects
Architectenassociatie (P. Bontenbal)
completed in 2007
complete design
Height:
Function:
Floor Space:
Customer:
Architect:
Status:
Deerns:
98 m (322 ft)
office space
approx. 32,600 m2 (350,900 sq ft) GFA
G&S Vastgoed
Toyo Ito (Japan)
completed in 2004
complete design
Height:
Function:
Floor Space:
Customer:
Architect:
Status:
Deerns:
96 m (315 ft)
office space
approx. 29,200 m2 (314,310 sq ft) GFA
Mahler4 Consortium
Rafael Viñoly (Italy)
completed in 2004
master plan and preliminary design
Height:
Function:
Floor Space:
Customer:
Architect:
Status:
Deerns:
88 m (289 ft)
residential
approx. 31,700 m2 (341,215 sq ft) GFA
Mahler4 Consortium
de Architecten Cie.
under construction (2007)
master plan and preliminary design
Erasmus MC Faculty Tower, Rotterdam
Willemswerf, Rotterdam
Height:
Function:
Floor Space:
Customer:
Architect:
Status:
Deerns:
88 m (289 ft)
office space
approx. 35,000 m2 (376,740 sq ft) GFA
Koninklijke Nedlloyd Group
W. Quist
completed in 1988
complete design
Height:
Function:
Floor Space:
Customer:
Architect:
Status:
Deerns:
112 m (367 ft)
university
approx. 65,000 m2 (699,650 sq ft)
Erasmus MC
A. Hagoort & G. Martens
completed in 1968, renovated
2006–2008
renovation of various laboratories,
logistics study and elevator renovation
Deerns consulting engineers
P.O. Box 1211
2280 CE Rijswijk (The Hague)
T +31 (0)70 395 74 00
F +31 (0)70 319 10 71
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www.deerns.com
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